42 research outputs found
Perfect absorption in mirror-symmetric acoustic metascreens
Mirror-symmetric acoustic metascreens producing perfect absorption
independently of the incidence side are theoretically and experimentally
reported in this work. The mirror-symmetric resonant building blocks of the
metascreen support symmetric and antisymmetric resonances that can be tuned to
be at the same frequency (degenerate resonances). The geometry of the building
blocks is optimized to critically couple both the symmetric and the
antisymmetric resonances at the same frequency allowing perfect absorption of
sound from both sides of the metascreen. A hybrid analytical model based on the
transfer matrix method and the modal decomposition of the exterior acoustic
field is developed to analyze the scattering properties of the metascreen. The
resulting geometry is 3D printed and experimentally tested in an impedance
tube. Experimental results agree well with the theoretical predictions proving
the efficiency of these metascreens for the perfect absorption of sound in the
ventilation problems
Physical and biological processes at the Subtropical Convergence in the South-west Indian Ocean
A detailed hydrographic and biological survey was conducted in the region of the Subtropical Convergence in the Indian sector of the Southern Ocean in April 2007. Hydrographic data revealed that the subsurface expression of the Subtropical Convergence (at 200 m), marked by the 10°C isotherm, appeared to meander considerably between 41°S and 42°15'S. Total surface chlorophyll-a concentration was low and ranged from 0.03 to 0.42 Όg l-1 and was always dominated by the pico- ( 0.05). The Zooplankton community was dominated, numerically and by biomass, by mesozooplankton comprising mainly copepods of the genera, Oithona, Paraeuchaeta, Pleuromamma, Calanus and Clausocalanus. An exception was recorded at those stations in the region of the front where the tunicate, Salpa thompsoni, dominated the total Zooplankton biomass
Life history traits influence in gonad composition of two sympatric species of flatfish
AbstractParalichthys orbignyanus and Paralichthys patagonicus are flatfish with different life history traits, having in common the condition of breeding in seawater. Paralichthys patagonicus remain their whole life in open seawater and Paralichthys orbignyanus are sometimes found in brackish water bodies. As marine and estuarine food webs have different fatty acid (FA) compositions, the aim of this study was to characterize the gonadal maturation of P. orbignyanus and P. patagonicus females through the analysis of lipid content and FA profile in order to understand to what extent life history traits are reflected in the ovarian composition. During gonadal maturation lipid content increased and FA profiles changed in both species, but the lipid increase was greater in P. orbignyanus. The N-3FA and n-3HUFA proportions increased in both species but were higher in P. orbignyanus. The differences between the lifestyles of these species were reflected in the ovarian FA profile mainly as a result of differences in their FA metabolism, causing a greater accumulation of n-3FA and n-3HUFA in P. orbignyanus than in P. patagonicus. The higher lipid accumulation in P. orbignyanusâ ovaries could indicate that this species, feeding in brackish water bodies, has the possibility of storing more energy than P. patagonicus